This invention is an improvement to catamaran planing boats of the type described in my U.S. Pat. No. 3,709,179. This type of boat owes its smooth ride in waves to having no more planing bottom surface than necessary to support its weight at cruise speed, in combination with substantially vertical sides. When a wave passes, the boat experiences little vertical force.
Early models, such as shown in U.S. Pat. No. 3,709,179, were designed to go rather fast for their size, i.e., to operate at a high Froude number. The desire has since arisen to make such a boat larger, but without a comensurate speed increase. I.e., the larger boat is to operate at a lower Froude number.
Ordinarily, this would entail a change of shape. The hulls would become wider at the sterns, so as to have more planing surface. This has the disadvantage of increasing the boat's waterplane area, hence its sensitivity to waves. It would be better to retain a shape closer to the original, while increasing the planing surface some other way.
There were also difficulties with the early boats. They were inconveniently sensitive to trimming moments from whatever cause, even when planing. For instance, they trimmed excessively bow up in strong head winds, and would tolerate little shifting of weight fore and aft. In smooth water, they sometimes porpoised.